Bisphosphonate-associated osteonecrosis of the jaw (ONJ) adversely affects the quality of life and produces significant morbidity in afflicted patients. It is characterized by the finding of exposed alveolar bone in the oral cavity. The risk of ONJ in patients with cancer treated with high doses of intravenous bisphosphonates (Pamidronate and Zolendronic acid) is higher, ranging from 1 to 10 %, compared to patients with osteoporosis treated with low dose, oral bisphosphonates (0.00001 to 0.0001 %). It has been assumed that the primary lesion for ONJ lies in bone and is related to over-suppression of bone turnover. However, it is unclear why these lesions present with loss of the oral mucosal covering of the mandible or maxilla as the primary clinical feature. A possible explanation of this symptom is that bisphosphonates are accumulated in bone in concentrations sufficient to be directly toxic to the oral mucosa and result in the failure of healing of soft tissue lesions, leading to the pathogenesis of ONJ. In addition, tooth extraction is the dominating event preceding ONJ, although other causes such as periodontal disease, dental implant procedures, exostoses, and ill-fitting dentures are also preceding factors for ONJ. Moreover, an anti-angiogenic effect of bisphosphonates has been reported recently. Since sufficient reconstitution of vasculature is prerequisite for wound healing, suppression of angiogenesis may result in the failure of healing of soft tissue lesions leading to the pathogenesis of ONJ. Although, these findings suggest involvement of bisphosphonate on oral mucosa in the development and/or progression ONJ, the effect of intravenous bisphosphonates on oral mucosa has not been studied in vivo. Our overall hypothesis is that intravenous bisphosphonates may inhibit healing of oral mucosa and contribute to the development and/or progression ONJ. We plan to elucidate the relationship between bisphosponates and the oral mucosa by testing the following Aims. In Aim 1, we will determine the cytotoxic effect of intravenous bisphosphonate, zoledronic acid, on oral mucosa, in vivo, during the wound healing process after tooth extraction in a rat model, by utilizing basic histology and the live/dead cell vitality assay. The aim will demonstrate the cytotoxic effect of zoledronic acid during healing of oral mucosa after tooth extraction. In Aim 2.1, we will determine if reconstitution of the vasculature in the oral mucosa is altered by zoledronic acid during the healing process after a tooth extraction, using immunofluorescence method. In Aim 2.2 we will further investigate whether the alternation of vasculature reconstitution is due to suppression of angiogenic and hypoxia related gene expression. The aim will demonstrate the anti-angiogenic effect of zoledronic acid during healing of oral mucosa after tooth extraction, in vivo. If successful, the proposed experiments will advance research that will fill a current knowledge gap in characterization of molecular mechanisms of action of intravenous bisphosphonates on oral soft tissues that may subsequently lead to the understanding of pathophysiology of development and/or progression of bisphosphonate-associated ONJ. PUBLIC HEALTH RELEVANCE: Bisphosphonate-associated osteonecrosis of the jaw (ONJ) is characterized by the finding of exposed alveolar bone in the oral cavity and adversely affects the quality of life and produces significant morbidity in afflicted patients. The underlying pathogenesis of ONJ is yet to be clearly elucidated. The proposed experiments will advance research that will fill a current knowledge gap in characterization of molecular mechanisms of action of intravenous bisphosphonates on oral soft tissues that subsequently lead to the understanding of pathophysiology of development and/or progression of bisphosphonate-associated ONJ.